Commercially available clear pressure sensitive label (PSL) films work very well for printing applications, but some currently used coatings for such films contains VOCs that constrain the allowed coating weights in certain countries. An example of a clear film used in PSL is Label-Lyte™ 50 LL539. Cost pressures have driven some roll-stock laminators that use pre-siliconized liners to use low-cost liners that have high levels of free silicone. When laminated to these liners with relatively high levels of free silicone, certain films do not perform well. Therefore, what is needed is a film coating that is essentially VOC-free that can also tolerate lamination to liners having higher levels of free silicone.
There have been progressive changes and improvements in printable film coatings. U.S. Pat. No. 6,893,722 discloses the use of an amine functional styrenated polyacrylate-based coatings with unsaturation to enhance cross-linking that demonstrates improved printability on polypropylene films. WO 2012-134695 describes film coatings that retain some essential elements of U.S. Pat. No. 6,893,722 that yield excellent UV printability and print durability (isopropyl alcohol resistance, pasteurization resistance, etc.) but without VOCs and without the need of a complex polymerization process (and the associated equipment constraints). However, further tests of coatings described in WO 2012-134695 showed significantly worse print performance in instances in which the printable coating was exposed to a silicone release liner, and the performance was worse than films made for such printing, especially if the printer used on-press corona treatment to cross-link the excess silicone coming from the low-cost liners. A key element taught in WO 2012-134695 is modification of a polyalkyleneimine (PAI) backbone in such a way to yield a dry coating that contained moieties of ethenic unsaturation from the group consisting of acrylic, methacrylic, and enamine. The present disclosure is to a different kind of modification of PAI polymers by reacting glycidyl ethers of ethoxylated long-chain alcohols and other such modifiers with primary and secondary amines in the PAI backbone.
Other related publications include U.S. Pat. No. 7,086,732; U.S. Pat. No. 6,866,383; U.S. Pat. No. 6,503,989; U.S. Pat. No. 6,428,878; U.S. Pat. No. 6,297,328; U.S. Pat. No. 5,296,530; U.S. Pat. No. 5,525,662; U.S. Pat. No. 5,498,659; U.S. Pat. No. 5,811,121; U.S. Pat. No. 5,380,587; U.S. Pat. No. 5,382,473; U.S. Pat. No. 5,419,960; U.S. Pat. No. 5,789,123; U.S. Pat. No. 5,827,627; US 2011/0254909; and US 2007/0248810; EP 1,502,759; EP 1,148,104; and the data sheet for Epomin™ polyethyleneimine from Nippon Shokubai, 2011.